In the past, lumbar adjustment assemblies have been employed in vehicle seats to enable a seat occupant to adjust part of a vehicle seat, namely part of the backrest, to provide a desired amount of lumbar support for comfort. U.S. Pat. Nos. 4,564,235; 5,588,703; 5,505,520; 5,718,476; and 6,688,690, are a few examples of adjustable seat occupant support assemblies that are used to provide adjustable lumbar support to a seat occupant.
With reference to FIG. 1, manufacturers of seats that incorporate lumbar adjustment assemblies have used in the past, or are currently using, a conventional steel frame backrest. In one such lumbar adjustment system 20 shown in FIG. 1, the backrest frame (not shown) has structural cross members 22, which partially constrains one end of a centrally located, generally convex-bowed, flexible plate 24. This plate 24, which is typically made of steel or plastic, bears against foam (not shown) in the seat that is located in the backrest between the plate 24 and the back of a seat occupant (not shown). This plate 24 is acted upon by a threaded rod 26, which is axially fixed to the backrest frame, and a threaded nut-like element 28 that engages the free end of the convexly-bowed plate 24. As the rod 26 is rotated, the nut translates along the rod 26, which moves the free end of the convexly-bowed plate 24 relative to the constrained end. This increases or decreases the amount of the bow or curvature in the convexly-bowed plate 24. As the bow or curvature in the plate 24 changes, it changes the amount by which it displaces and applies pressure against the backrest foam toward or away from the lumbar region of a seat occupant. A load distribution pad (not shown) can be located between the convexly-bowed plate 24 and the backrest foam to help spread the force applied by the plate 24 to the foam more evenly along the foam. Manipulation of the backrest foam in this manner by changing the amount of bow or curvature in the convexly-bowed plate 24 changes the shape of and/or the amount of support provided by the backrest to the lumbar region of a seat occupant.
Although not shown, there is another more complex lumbar adjustment system that is also commonly used in seats with conventional steel backrest frames. This system is self-contained and is generally mounted to a backrest cross member with threaded fasteners. It includes a vertically-oriented, convex-shaped, cross-lattice element that is manufactured using steel or plastic strip material. The convex shape of the cross-lattice element is curved toward the backrest foam. This basic system is used with a variety of mechanisms to change the shape of the cross-lattice element. Any of these can be functionally illustrated by analogy using a simple archer's bow, with the bow representing the cross-lattice element, and the bow string representing the mechanism that controls the amount of arch, bow or curvature of the lattice element. As the ends of the lattice element are brought closed together, typically using a tensile member, the convex shape of the lattice element increases. Conversely, as the tensile element is relaxed the shape flattens out. The lattice type element generally bears directly on the foam of the backrest. Again, this manipulation of the backrest foam changes the shape of and/or the support provided by the lumbar region of the backrest.
A further type of lumbar adjustment system incorporates an inflatable air bladder positioned between a support element and the foam in a typical steel frame seat backrest. An example of such a system is shown in FIG. 20 of U.S. Pat. No. 5,658,050. One variant includes a hand squeezed bulb to pump up the bladder to increase its cross section, and an inline needle type valve that can opened to decrease the pressure in the bladder and reduce its cross section. Typically the bladder acts directly on the foam in the seat backrest. Again, manipulation of the backrest foam changes the shape of and/or the support provided by the lumbar region of the backrest.
While many of these adjustable seat occupant support assemblies and systems have enjoyed commercial success in the past, their complexity and cost has prohibited their application to lower cost off-road vehicle seating.